1. K. Tsiolkovsky, The Exploration of Cosmic Space by Means of Reaction Devices (In Russian: Issledovanie mirovih prostranstv reaktivnimi priborami): reissue of works in 1903 and 1911 with some changes and additions (Kaluga, 1926)
2. H. Potocnik, The Problem of Space Travel - The Rocket Motor (In German, Das Problem der Befahrung des Weltraums - der Raketen-Motor) (Berlin, 1929)
3. V. Kuznetsov, V. Sinelnikov, S. Alpert, Yakov Alpert: Sputnik-1 and the first satellite ionospheric experiment. Adv. Space Res. 55(12), 2833–2839 (2015). https://doi.org/10.1016/j.asr.2015.02.033
4. A. Tatem, S. Goetz, S. Hay, Fifty years of Earth-observation satellites. Am. Sci. 96(5), 390 (2008). https://doi.org/10.1511/2008.74.390
5. National Aeronautics and Space Administration (NASA) Space Science Data Coordinated Archive, https://nssdc.gsfc.nasa.gov/nmc/SpacecraftQuery.jsp. Accessed 1 Jun 2020